Janis Winehouse-Collins, 60, writes in her new memoir, Loving Amy: A Mother's Story, about the agony of seeing the "Rehab" singer, strained by the rigors of fame, change from a chatty little girl, with a "wonderful sense of humor" into a shadow of her former self.
But speaking to PEOPLE, Janis says that more than three years after Amy's death at age 27 on July 23, 2011, she has no regrets.
"There was nothing I could have done that was different," Janis says: "She wasn't the Amy that I know and brought up and that's what was horrible.
"Basically, it was the addiction that changed her."
Janis, who remarried family friend Richard Collins, 64, after Amy’s death, suffers from Multiple Sclerosis and says she wrote the book "while I still remember."
For an exclusive excerpt from Janis Winehouse-Collins' new book and much more from her interview, pick up a copy of PEOPLE on newsstands Friday.
Amy died from alcohol poisoning and Janis admits: "I was helpless, that’s the worst part. You want to be there, but we are limited with what we can do.
"But I was always there for her, I listened to her, she would phone me, we would speak, I was always there."
Loving Amy: A Mother's Story is out in hardcover on Jan. 12